3" down and 2.5" catback

[TurboBird]

Is it possible to do this: have a 3" down pipe and test pipe, with a 2.5" cat back? Has anyone done this? How well did it work?
I am just curious b/c I eventually want to go all 3", but I have heard you don't need 3" until you are like sub 12's and it may hinder the performance of these car b4 that.

 

[big green]

I would just get a full 3" to save the money. Why buy a part you know your going to replace?